Where'd the color come from

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Where'd the Color Come From, By Terry Cusick

Did you ever wonder how the ancestors to the goldfish and koi evolved into such colorful fish? After all, these fish were and still are between a silvery gray to olive brown in color. It turns out that these wild fish are born with four different kinds of pigment cells called chromatophores. These four chromatophores are melanin (black), xanthin (yellow), lipochrome (orange), and erythrin (red). Their wild color mostly comes from the black and yellow pigment cells. A common mutation of these wild carp is to be born without the black which gives the fish a golden color. It was no doubt this mutation that first started humans keeping these fish. However, goldfish and koi come in a lot more colors than black, yellow, orange, and red. All the other colors are based on these 4 colors, it just depends on the concentration of color pigment cells and how close the cells are located to the surface of the fish’s dermal layer. For example blue is the black pigment in low concentrations and deep in the dermal layer. The lack of any chromataphores results in white. There is one other thing that slightly modifies these colors and that is the reflexivity of the fish. The reflexivity of the fish comes from the position of the irridocytes within the skin. The irridocytes are tiny reflective spheres. If the irridocytes are on the surface of the scales the fish is said to have a metallic finish or what the Japanese call "hikari". If the irridocytes are deeper in the dermal layer, the fish is said to have a mat finish or what the Japanese call "kawari".

Often as a fish ages their colors will change. This is especially true with koi. The reason is due to the fact that each fish is born with a fixed number of chromatophores which remains relatively constant throughout its life. As the fish grows, these chromatophores have to cover a larger area of skin. If the chromatophores are thin, for instance, just covering the surface of the skin, a young fish will look like they have strong color in a particular area. However, as the fish grows, the color in that area spreads and appears to breakup revealing the underlying color. Sometime, when the pigments are just on the surface of the skin, they will disappear altogether. A fine example of this is a young goldfish with a light colored underside and a black back like a Panda Goldfish. All the black will disappear by the time the fish is three years old. Conversely, if the chromatophores are present in all the layers of the skin, on the surface of the skin (above the scales), immediately under the scales and deep in the skin, as the fish grows, the color will continue to appear dense and will be stable. At this point you maybe asking yourself "How do you know whether a young fish has thick or thin color?". The answer is "you don’t". Knowing the parents helps and this is why koi from good bloodlines bring premium prices over koi of questionable background.

There are conditions that will temporarily effect the color of your fish. To understand how this temporary change happens, you need to understand the chromatophore. A chromatophore is a branched cell, within which the color pigment can be moved. The two extremes are that the pigment spreads though out the entire cell which results in the fish having great color or it is concentrated in one small spot in the center resulting in the loss of color in the fish. Some of the conditions that effect this concentration are:

Raised levels of pollutants (e.g. ammonia, nitrite or nitrate) will cause the pigment to contract.

pH and hardness affect coloration differently, red pigment tends to spread in softer, more acidic water, whereas black pigment spreads in harder more alkaline water and vice versa.

Background colors - Although it is difficult to merge into the background when you are a red and white Koi, they do try to do so. Against a pale background the fish contract the pigment to make themselves as, pale as possible. The opposite occurs when the fish is next to a dark background, which is why blue vats are used at Koi shows to ensure each Koi looks its best.

Salt added to the water causes the pigment to concentrate.

Medications like antibiotics, whether added to the water or injected and malachite green based remedies negatively effect color.

Temperature - At high summer temperatures pigments contract; at cool autumn and winter values they expand resulting in the fish looking at their best in the cooler months of the year.

Finally, what can you do to improve the color of your fish? That is other then avoid the aforementioned conditions. What you feed them. Fish cannot synthesize their own color pigment and therefore they have to consume it. Therefore it is important to feed color-enhancing foods. As with all Koi feeds, it is important that the color enhancing food given be of the highest quality to ensure that the pigments are in a form that the fish can absorb into its body. If color foods are not given to your fish, the chromatophores would not be filled with pigment and the Koi will look pale or poorly colored. This can result in a fish of high potential quality only looking mediocre. Feeding a color food would greatly enhance the appearance of such a fish - but could not make a poor fish great. You can not give your fish too much color food for when the chromatophores are filled with pigment, the excess is passed through the feces. It is possible to get white areas of the fish to become pink due to a temporary build up of rythrin. This pigment is not in a chromatophore and will quickly disappear as soon as the amount of color food given is reduced.

So the next time you’re watching your fish swimming around, think about its color and what you can do to enhance it. Good Luck!